This invention relates to the art of attaching articles to a printed circuit board. The invention is particularly applicable in the attachment of power transistors and their associated heat sinks to printed circuit boards made of fibrous material.
Generally printed circuit boards are made of fiber reinforced plastic. Large amounts of rather delicate and thermally sensitive circuitry are disposed on the surface of the boards. The use of fibrous material arranged generally parallel to the plane of the board tends to minimize the effects of thermal expansion and contraction upon inplane circuitry. However, the coefficient of thermal expansion in a direction perpendicular to the plane of the panel is increased significantly as a result. And, therefore, firmly attaching articles to printed circuit boards has been a problem. The problem is particularly acute in the case of power transistors and their associated heat sinks, because in order for the heat sink to dissipate sufficient amounts of heat, close and continuous contact must be maintained between the power transistor and the heat sink. The problem is compounded by the fact that power transistors by design undergo frequent thermal cycling. This cycling causes expansion and contraction of neighboring materials. As a result both thermal and electrical conductivity may be impaired.